The present invention relates to a piezoelectric actuator control system, in particular for the fuel injectors of a Diesel engine.
Fuel injection systems with valves or fuel injectors operated by piezoelectric actuators have been proposed for some years but are still afflicted by numerous problems. These problems mostly involve the particular properties of piezoelectric actuators and have delayed the development of these systems compared to that of more conventional and more easily controlled arrangements, based on the use of fuel injectors or valves using electromagnets.
A number of the problems which affected systems using piezoelectric actuators have been solved, but only by means of arrangements which were very complex and/or expensive to implement and which have held up the wider application of piezo-electric fuel injectors.
Without attempting to list all the problems affecting such systems, the main disadvantages included:                tolerances in the performance of different fuel injectors, stability of performance and long term recalibration of characteristics;        variations in the “size” of fuel injectors of different power;        problems with replacing items in service in the event of malfunction and set-up problems during manufacture;        complexity of the wiring systems, problems of safety of operatives (high voltages), emissions of electromagnetic radiation and electromagnetic susceptibility;        difficulties in carrying out multiple fuel injections close together, in achieving temporally superimposed fuel injections (in different cylinders), and in controlling the partial opening of the fuel injectors, and problems in starting the engine; and        the need to rationalize circuits of the control, operating and diagnostic systems.        